1. Field of the Invention
This invention relates to rheologically modified scleroglucan compositions that can be used as insulating fluids. These compositions advantageously demonstrate long term stability to high temperatures and metal ion contaminants.
2. Background of the Invention
The conveyance of oil obtained from offshore fields requires specially designed systems. Sometimes, the temperature of oil, pumped from beneath the ocean floor, is about 104.degree.-121.degree. C. (220.degree.-250.degree. F.). The temperature of the water through which the oil must be conveyed can be as low as 0.degree.-10.degree. C. (32.degree.-50.degree. F.). Any system for conveying oil through such a low temperature environment must provide a suitable means for insulating the oil from the low temperature of the surrounding environment.
Failure to provide adequate insulation results in reduction of the oil temperature. It is important to maintain high oil temperature to retain low viscosity and high pumpability of the oil as it is pumped through the pipeline. As the temperature decreases, the viscosity of the oil increases making it more difficult to pump. Further, at lower temperatures, separation and crystallization of the various hydrocarbon fractions present in the oil may result. For example, paraffins, low viscosity hydrocarbons, medium viscosity hydrocarbons, oil sludge, and the like, may deposit on the pipeline walls gradually restricting oil flow. Thus, the means of conveyance, typically pipelines, must be insulated to achieve efficient flow of the oil.
Means of insulating oil pipelines are known. For example, Ramsay, et al., U.S. Pat. No. 5,290,768, describes the use of welan gum/ethylene glycol compositions as insulating compositions for oil pipelines. A chelating agent, such as ethylenediamine tetraacetic acid, is present in these compositions to minimize the deleterious effects of metal ion contaminants present in pipeline pumping operations.
Scleroglucan compositions have been used in oil recovery operations. Donche, et al., U.S. Pat. No. 5,306,340 describes cementation spacers for use in oil drilling operations composed of aqueous based compositions of unrefined scleroglucan, wherein the scleroglucan contains at least 15% mycelium. These aqueous based compositions contain 0.1% to 2% scleroglucan/mycelium and may additionally contain 1% to 10% polyol or dialdehyde; the balance of the compositions being water. The polyol-containing aqueous compositions may be prepared by dispersing a paste, composed of scleroglucan/mycelium and polyol, in water. Generally, the paste is comprised of 10 to 30% scleroglucan (containing at least 15% mycelium), 70 to 90% polyol and 0 to 10% water. The high relative concentration of scleroglucan in the paste provides a mixture wherein the scleroglucan particles are coated, but not solvated by the polyol. These scleroglucan pastes, as described in this reference, would not be effectively pumpable and thus, would not be useful as oil pipeline insulating materials.
Although the aqueous based scleroglucan compositions of Donche are reportedly effective as cementation spacers during oil drilling operations, such compositions are incompatible with insulation applications, wherein the operating temperatures are often much higher than the boiling point of water. Additionally, the high water content of these compositions would have a very corrosive effect on the metal pipes used in oil pipeline operations.
Accordingly, a rheologically modified composition that functions as an effective insulating material, is non-corrosive, and demonstrates long term stability to high temperatures and metal ion contaminants would be highly desirable for oil pipeline insulation applications.